Metal has been the most frequently used material for a heat radiating member such as the main body, chassis or heat radiating plate of most electronic equipment having exothermic parts. This is because metal has high thermal conductivity such that it can diffuse heat more quickly to the surroundings than other materials so as to protect electronic parts that are sensitive to heat from local high temperatures. Moreover, metal has high mechanical strength and also workability via plating, molding or cutting such that it can be appropriately used as a material for a heat radiating member which typically has a complex shape. However, metals have disadvantages, such as their high density which make it difficult to make the metal lightweight, and the high unit price thereof. Because of these disadvantages of metal, there has been a focus on thermally conductive resins to replace metal as a material for heat radiating members. As a result, heat radiating members such as heat radiating sheets or heat radiating grease using a thermally conductive resin have been used for printers, copying machines, notebook computers and the like.
Recently, as electronic equipment becomes highly integrated and efficient, more heat is generated in the electronic equipment. Moreover, as electronic equipment becomes thinner and lightweight, it is even more difficult to diffuse heat generated in the electronic equipment to the surroundings. As a result, the local high-temperature state resulting from heat generated in the electronic equipment, which can lead to a malfunction or a fire, has increasingly become a problem. However, the thermal conductivity of the thermally conductive resins developed up to date is not enough to solve this problem.
Furthermore, when increased amounts of thermally conductive filler are added to a thermally conductive resin to improve thermal conductivity of the resin composition, the injection moldability of the thermally conductive resin deteriorates so that the manufacture of a product using the same becomes more difficult. Moreover, the mechanical strength of a product manufactured using the thermally conductive resin also deteriorates. Therefore, it is important to form an effective network of fillers in a resin composition in order to minimize the amounts of fillers and maximize the thermal conductivity at the same time. Furthermore, a resin having low viscosity should be used in order to prevent the deterioration of injection moldability when the fillers are added in large amounts.
Typically, a resin having low viscosity should have a low molecular weight. When the molecular weight of the resin is low, however, reactivity between polymer chains can increase and some side effects such as progress of hardening due to reaction in extrusion and injection molding processes can occur.
Accordingly, it is important to form an effective network of fillers in a resin matrix in order to produce a thermally conductive resin composition which can be injection-molded and is important to improve filling with the fillers by reducing the viscosity of the resin. Furthermore, it is also important to stabilize color and other mechanical properties (processing stability) when the resin stays in a cylinder of molding machine such as an injection molding machine for a long time.